1. Field of the Invention
The present invention relates to receptacle filling machines, and more particularly to improvements in the valve control mechanisms of positive displacement rotary filling machines.
2. Description of the Prior Art
Rotary filling machines employing reciprocable pistons to effect positive discharge of product from a turret of cylinders through discharge nozzles associated with each cylindeer into receptacles fed into a filling arc; i.e., that portion of a receptacle's travel during which it is positioned beneath a discharge nozzle, are well known and widely used.
Such machines generally comprise a vertically reciprocable plunger valve associated with each cylinder, which, in one of its two positions, opens communication between the cylinder and a product reservoir, and in the other position opens communication between the cylinder and the discharge nozzle.
In order to prevent the discharge of product when no receptacle is present beneath a discharge nozzle, various "no can no fill" mechanisms have been developed. These mechanisms sense the presence or absence of receptacles and control the associated valve so that if no receptacle is present beneath a given discharge nozzle, the discharge stroke of the piston will return the cylinder's content to the product reservoir instead of discharging it through the discharge nozzle.
Kerr U.S. Pat. No. 2,958,346 disclosed two forms of "no can no fill" mechanisms, one employing a vertically reciprocating valve structure and the other a rotary valve structure. In both mechanisms the valve actuator is operated by a fixed cam, but does not actuate its associated valve unless a receptacle detector adjacent each receptacle position detects a receptacle in that position ready to be filled.
Minard U.S. Pat. No. 3,097,672 discloses a "no can no fill" mechanism in which the cam for operating the valve actuator has a displaceable entry ramp which can be lowered to prevent operation of one or more of the valve actuators by the cam. Displacement of the entry ramp is controlled by a single receptacle detector which causes lowering of the ramp when no receptacle is detected in the first position within the filling arc.
In order for such arrangements to function satisfactorily, the actuator-to-valve latching mechanism of Kerr or the entry ramp mechanism of Minard must be controlled and positioned in the space between filling stations; for, if there is only one receptacle missing in the line being fed to the machine, the "no can no fill" mechanisms must be set to "no can" condition for the missing receptacle and returned to normal condition for the next one.
Since the piston operating cam cannot be allowed to initiate the discharge stroke of the piston until the "no can no fill" mechanism has been set, and such setting cannot take place until a receptacle has been fed into the filling arc or the absence of one has been detected therein, the portion of the filling arc within which products can be actually discharged into a receptacle necessarily is reduced.
On the latest high speed machines, filling stations are spaced as closely together as four inches (10.16 cm) center to center, and generally a valve lift of at least 3/4 of an inch (1.91 cm) is required to properly position the valve.
Since speeds of 1200 receptacles per minute are not uncommon today on 36 station filling machines, it will be seen that it has become almost impossible to design a "no can no fill" mechanism of the above described types which will operate in such a short distance at such speeds without any valve being improperly positioned, causing a very irregular filling pattern.